THE SKELETON AND TEETH 125 muscles take origin; and several foramina are seen on this surface of the mandible, the largest being in the floor of the genial fossa. There is only one mental foramen on the exterior of the body of the mandible. Below the genial fossa the halves of the mandible are united by a ledge of bone known as the simian shelf. The mylo-hyoid ridge is small. THE GORILLA. (Pig. 24).* The skull of the Gorilla resembles that of the Chimpanzee in many points in which both differ from the skulls of the Asiatic Simiidse. And there are some features in which it resembles the skull of Man and differs from those of all other Apes. The skull is absolutely larger than that of the Chimpanzee, and the facial part is relatively larger than the cranium. The sexual differences too are greater, the female cranial cavity being 85 per cent, of that of the male, whereas it is 95 per cent, in the Chimpanzee. Norma Frontalis.—When the skull of an adult male is viewed from the front two features become obvious at once. The temporal ridges converge on the frontal bone behind the massive supra-orbital crests and unite to form a high sagittal crest. The only other Ape which exhibits a sagittal crest is the adult male Orang, but it is never as large as in the Gorilla. The crests and ridges increase as age advances * The skull has been describe-i in whole or in part in papers 14, 15, 17, 20, 44, 50, 53> 59: 87, 92, 109, 122, 343, 405* 4*«, 426, 43'. 440, 447* 45», 452. 45<5, 4^0, 461, 480, 481, 485, 499> goo, 502, 503, 505, 506.